VOLATILE SIGNALS OF THE MAJOR HISTOCOMPATIBILITY COMPLEX IN MALE-MOUSE URINE

Variation in the gents of the major histocompatibility complex (MWC) c ontributes to unique individual odors (odortypes) in mice, as demonstr ated by the ability of trained mice in a Y-maze olfactometer to discri minate nearly identical inbred mice that differ genetically only at th e MHC (MHC congenic mice), while they cannot distinguish genetically i dentical inbred mice, Similar distinctions are possible with urine, a substance that is involved in many facets of mouse chemical communicat ion, This paper reports results supporting the hypothesis that the MHC -determined urinary odor is composed of a mixture of volatile carboxyl ic acids occurring in relative concentrations that are characteristic of the odortype, Y-maze behavioral testing of urine fractions from ani on exchange chromatography indicates that volatile acids are necessary and sufficient to convey MHC odortype information. Diethyl ether extr acts, which are expected to contain the more volatile, less polar orga nic acids, were also discriminable in the Y-maze olfactometer, Ether e xtracts of 12 different urine samples from each of two panels of MHC c ongenic mice were analyzed by gas chromatography. No compounds unique to urine of either genotype mere detected, but compounds did appear to occur in characteristic ratios in most of the samples of each type, N onparametric statistical analysis of the gas chromatographic data show ed that eight of the peaks occurred in significantly different relativ e concentrations in the congenic samples, One of the peaks was shown t o represent phenylacetic acid, which has implications for the mechanis m of the MHC specification of odortype.